You can link a P3P controller to any P3P drone ... as you can link any P3S controller to any P3S drone ...
What happens is the Controller and Drone exchange Coded ID and then they are locked to each other. Until you decide to lock to another unit etc.
What people tend to forget is :
All same frequency controllers are heard / received by same frequency receivers / drones. But because of the ID code that identifies the data string - it only reacts to the locked paired data string and rejects the others. The strings of data are transmitted many times a second and this then means that it can reject corrupt strings without losing control because another set of data is already being sent ...